Downlink coverage enhancements

ABSTRACT

Aspects of the present disclosure provide techniques and apparatus for enhancing downlink coverage for certain user equipments (UEs) (e.g., low cost, low data rate UEs). Certain types of UEs may have limited coverage or should receive enhanced coverage relative to other types of UEs. For example, some types of low cost UEs may have only a single receive chain, thereby limiting DL coverage, while other types of UEs benefit from multiple receive chains. One example method generally includes identifying a first type of one or more UEs that is to receive enhanced downlink (DL) coverage relative to a second type of UEs and utilizing one or more DL coverage enhancement techniques when communicating with the first type of UEs, the one or more DL coverage enhancement techniques designed to adjust at least for reduced DL processing gain of the first type of UEs relative to the second type of UEs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Patent ApplicationSer. No. 61/681,902, entitled “Downlink Coverage Enhancements” and filedAug. 10, 2012, which is herein incorporated by reference.

BACKGROUND

I. Field

Certain aspects of the present disclosure generally relate to wirelesscommunications and, more particularly, to techniques and apparatus forincreasing downlink (DL) coverage to certain types of user equipments(UEs).

II. Background

Wireless communication systems are widely deployed to provide varioustypes of communication content such as voice, data, and so on. Thesesystems may be multiple-access systems capable of supportingcommunication with multiple users by sharing the available systemresources (e.g., bandwidth and transmit power). Examples of suchmultiple-access systems include code division multiple access (CDMA)systems, time division multiple access (TDMA) systems, frequencydivision multiple access (FDMA) systems, 3rd Generation PartnershipProject (3GPP) Long Term Evolution (LTE) including LTE-Advanced systemsand orthogonal frequency division multiple access (OFDMA) systems.

Generally, a wireless multiple-access communication system cansimultaneously support communication for multiple wireless terminals.Each terminal communicates with one or more base stations viatransmissions on the forward and reverse links. The forward link (ordownlink) refers to the communication link from the base stations to theterminals, and the reverse link (or uplink) refers to the communicationlink from the terminals to the base stations. This communication linkmay be established via a single-input single-output, multiple-inputsingle-output or a multiple-input multiple-output (MIMO) system.

SUMMARY

Certain aspects of the present disclosure generally relate to enhancingdownlink coverage for certain types of user equipment (UE) (e.g., lowcost, low data rate UEs).

Certain aspects of the present disclosure provide a method for wirelesscommunications by a base station. The method generally includesidentifying a first type of one or more UEs that is to receive enhanceddownlink (DL) coverage relative to a second type of UEs and utilizingone or more DL coverage enhancement techniques when communicating withthe first type of UEs, the one or more DL coverage enhancementtechniques designed to adjust at least for reduced DL processing gain ofthe first type of UEs relative to the second type of UEs.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes means foridentifying a first type of one or more UEs that is to receive enhancedDL coverage relative to a second type of UEs and means for utilizing oneor more DL coverage enhancement techniques when communicating with thefirst type of UEs, the one or more DL coverage enhancement techniquesdesigned to adjust at least for reduced DL processing gain of the firsttype of UEs relative to the second type of UEs.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes at least oneprocessor and a memory coupled to the at least one processor. The atleast one processor is typically configured to identify a first type ofone or more UEs that is to receive enhanced DL coverage relative to asecond type of UEs and to utilize one or more DL coverage enhancementtechniques when communicating with the first type of UEs, the one ormore DL coverage enhancement techniques designed to adjust at least forreduced DL processing gain of the first type of UEs relative to thesecond type of UEs.

Certain aspects of the present disclosure provide a computer programproduct for wireless communications. The computer program producttypically includes a computer-readable medium having instructions storedthereon. The instructions are generally executable by one or moreprocessors for identifying a first type of one or more UEs that is toreceive enhanced DL coverage relative to a second type of UEs and forutilizing one or more DL coverage enhancement techniques whencommunicating with the first type of UEs, the one or more DL coverageenhancement techniques designed to adjust at least for reduced DLprocessing gain of the first type of UEs relative to the second type ofUEs.

Certain aspects of the present disclosure provide a method for wirelesscommunications by a UE. The method generally includes receiving, by theUE which is of a first type of UEs that is to receive enhanced DLcoverage relative to a second type of UEs, information regarding one ormore DL coverage enhancement techniques utilized by a base station whencommunicating with the UE to adjust at least for reduced DL processinggain of the first type of UEs relative to the second type of UEs; andreceiving one or more downlink transmissions from the base station,transmitted utilizing the one or more DL coverage enhancementtechniques. For certain aspects, the method further includes processingthe one or more downlink transmissions based on the receivedinformation.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes means forreceiving, by the apparatus which is of a first type of UEs that is toreceive enhanced DL coverage relative to a second type of UEs,information regarding one or more DL coverage enhancement techniquesutilized by a base station when communicating with the apparatus toadjust at least for reduced DL processing gain of the first type of UEsrelative to the second type of UEs; and means for receiving one or moredownlink transmissions from the base station, transmitted utilizing theone or more DL coverage enhancement techniques.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes at least oneprocessor and a memory coupled to the at least one processor. The atleast one processor is configured to receive, by the apparatus which isof a first type of UEs that is to receive enhanced DL coverage relativeto a second type of UEs, information regarding one or more DL coverageenhancement techniques utilized by a base station when communicatingwith the apparatus to adjust at least for reduced DL processing gain ofthe first type of UEs relative to the second type of UEs; and to receiveone or more downlink transmissions from the base station, transmittedutilizing the one or more DL coverage enhancement techniques.

Certain aspects of the present disclosure provide a computer programproduct for wireless communications. The computer program producttypically includes a computer-readable medium having instructions storedthereon, the instructions executable by one or more processors forreceiving, by a UE which is of a first type of UEs that is to receiveenhanced DL coverage relative to a second type of UEs, informationregarding one or more DL coverage enhancement techniques utilized by abase station when communicating with the UE to adjust at least forreduced DL processing gain of the first type of UEs relative to thesecond type of UEs; and for receiving one or more downlink transmissionsfrom the base station, transmitted utilizing the one or more DL coverageenhancement techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram conceptually illustrating an example wirelesscommunication network, in accordance with certain aspects of the presentdisclosure.

FIG. 2 is a block diagram conceptually illustrating an example of anevolved node B (eNB) in communication with a user equipment (UE) in awireless communications network, in accordance with certain aspects ofthe present disclosure.

FIG. 3 is a block diagram conceptually illustrating an example framestructure for a particular radio access technology (RAT) for use in awireless communications network, in accordance with certain aspects ofthe present disclosure.

FIG. 4 illustrates two example subframe formats for the downlink with anormal cyclic prefix, in accordance with certain aspects of the presentdisclosure.

FIG. 5 illustrates example operations for enhanced downlink coveragethat may be performed by a base station, in accordance with certainaspects of the present disclosure.

FIG. 6 illustrates example operations for enhanced downlink coveragethat may be performed by a UE, in accordance with certain aspects of thepresent disclosure.

DETAILED DESCRIPTION

Aspects of the present disclosure provide techniques and apparatus forenhancing downlink coverage for certain user equipments (e.g., low cost,low data rate UEs).

For some systems, certain types of UEs may have limited coverage or, forsome reason, should receive enhanced coverage relative to other types ofUEs. For example, some types of low cost UEs may have only a singlereceive chain, thereby limiting DL coverage, while other types of UEsbenefit from multiple receive chains. Further, transmit power on adownlink may be limited, and/or a relatively narrow bandwidth may beused to communicate with these types of UEs, reducing frequencydiversity gains.

Techniques presented herein, however, may help enhance DL coverage tosuch UEs.

The techniques described herein may be used for various wirelesscommunication networks such as Code Division Multiple Access (CDMA)networks, Time Division Multiple Access (TDMA) networks, FrequencyDivision Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA)networks, Single-Carrier FDMA (SC-FDMA) networks, etc. The terms“network” and “system” are often used interchangeably. A CDMA networkmay implement a radio technology such as Universal Terrestrial RadioAccess (UTRA), cdma2000, etc. UTRA includes Wideband-CDMA (W-CDMA), TimeDivision Synchronous CDMA (TD-SCDMA), and other variants of CDMA.cdma2000 covers IS-2000, IS-95 and IS-856 standards. A TDMA network mayimplement a radio technology such as Global System for MobileCommunications (GSM). An OFDMA network may implement a radio technologysuch as Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDM®, etc. UTRA andE-UTRA are part of Universal Mobile Telecommunication System (UMTS).3GPP Long Term Evolution (LTE) and LTE-Advanced (LTE-A), in bothfrequency division duplex (FDD) and time division duplex (TDD), are newreleases of UMTS that use E-UTRA, which employs OFDMA on the downlinkand SC-FDMA on the uplink. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM aredescribed in documents from an organization named “3rd GenerationPartnership Project” (3GPP). cdma2000 and UMB are described in documentsfrom an organization named “3rd Generation Partnership Project 2”(3GPP2). The techniques described herein may be used for the wirelessnetworks and radio technologies mentioned above as well as otherwireless networks and radio technologies. For clarity, certain aspectsof the techniques are described below for LTE/LTE-A, and LTE/LTE-Aterminology is used in much of the description below.

An Example Wireless Communication System

FIG. 1 shows a wireless communication network 100, which may be an LTEnetwork or some other wireless network. Wireless network 100 may includea number of evolved Node Bs (eNBs) 110 and other network entities. AneNB is an entity that communicates with user equipments (UEs) and mayalso be referred to as a base station, a Node B, an access point (AP),etc. Each eNB may provide communication coverage for a particulargeographic area. In 3GPP, the term “cell” can refer to a coverage areaof an eNB and/or an eNB subsystem serving this coverage area, dependingon the context in which the term is used.

An eNB may provide communication coverage for a macro cell, a pico cell,a femto cell, and/or other types of cell. A macro cell may cover arelatively large geographic area (e.g., several kilometers in radius)and may allow unrestricted access by UEs with service subscription. Apico cell may cover a relatively small geographic area and may allowunrestricted access by UEs with service subscription. A femto cell maycover a relatively small geographic area (e.g., a home) and may allowrestricted access by UEs having association with the femto cell (e.g.,UEs in a closed subscriber group (CSG)). An eNB for a macro cell may bereferred to as a macro eNB. An eNB for a pico cell may be referred to asa pico eNB. An eNB for a femto cell may be referred to as a femto eNB ora home eNB (HeNB). In the example shown in FIG. 1, an eNB 110 a may be amacro eNB for a macro cell 102 a, an eNB 110 b may be a pico eNB for apico cell 102 b, and an eNB 110 c may be a femto eNB for a femto cell102 c. An eNB may support one or multiple (e.g., three) cells. The terms“eNB”, “base station,” and “cell” may be used interchangeably herein.

Wireless network 100 may also include relay stations. A relay station isan entity that can receive a transmission of data from an upstreamstation (e.g., an eNB or a UE) and send a transmission of the data to adownstream station (e.g., a UE or an eNB). A relay station may also be aUE that can relay transmissions for other UEs. In the example shown inFIG. 1, a relay station 110 d may communicate with macro eNB 110 a and aUE 120 d in order to facilitate communication between eNB 110 a and UE120 d. A relay station may also be referred to as a relay eNB, a relaybase station, a relay, etc.

Wireless network 100 may be a heterogeneous network that includes eNBsof different types, e.g., macro eNBs, pico eNBs, femto eNBs, relay eNBs,etc. These different types of eNBs may have different transmit powerlevels, different coverage areas, and different impact on interferencein wireless network 100. For example, macro eNBs may have a hightransmit power level (e.g., 5 to 40 W) whereas pico eNBs, femto eNBs,and relay eNBs may have lower transmit power levels (e.g., 0.1 to 2 W).

A network controller 130 may couple to a set of eNBs and may providecoordination and control for these eNBs. Network controller 130 maycommunicate with the eNBs via a backhaul. The eNBs may also communicatewith one another, e.g., directly or indirectly via a wireless orwireline backhaul.

UEs 120 (e.g., 120 a, 120 b, 120 c) may be dispersed throughout wirelessnetwork 100, and each UE may be stationary or mobile. A UE may also bereferred to as an access terminal, a terminal, a mobile station (MS), asubscriber unit, a station (STA), etc. A UE may be a cellular phone, apersonal digital assistant (PDA), a wireless modem, a wirelesscommunication device, a handheld device, a laptop computer, a cordlessphone, a wireless local loop (WLL) station, a tablet, a smart phone, anetbook, a smartbook, etc.

FIG. 2 is a block diagram of a design of base station/eNB 110 and UE120, which may be one of the base stations/eNBs and one of the UEs inFIG. 1. Base station 110 may be equipped with T antennas 234 a through234 t, and UE 120 may be equipped with R antennas 252 a through 252 r,where in general T≧1 and R≧1.

At base station 110, a transmit processor 220 may receive data from adata source 212 for one or more UEs, select one or more modulation andcoding schemes (MCSs) for each UE based on channel quality indicators(CQIs) received from the UE, process (e.g., encode and modulate) thedata for each UE based on the MCS(s) selected for the UE, and providedata symbols for all UEs. Transmit processor 220 may also process systeminformation (e.g., for semi-static resource partitioning information(SRPI), etc.) and control information (e.g., CQI requests, grants, upperlayer signaling, etc.) and provide overhead symbols and control symbols.Processor 220 may also generate reference symbols for reference signals(e.g., the common reference signal (CRS)) and synchronization signals(e.g., the primary synchronization signal (PSS) and secondarysynchronization signal (SSS)). A transmit (TX) multiple-inputmultiple-output (MIMO) processor 230 may perform spatial processing(e.g., precoding) on the data symbols, the control symbols, the overheadsymbols, and/or the reference symbols, if applicable, and may provide Toutput symbol streams to T modulators (MODs) 232 a through 232 t. Eachmodulator 232 may process a respective output symbol stream (e.g., forOFDM, etc.) to obtain an output sample stream. Each modulator 232 mayfurther process (e.g., convert to analog, amplify, filter, andupconvert) the output sample stream to obtain a downlink signal. Tdownlink signals from modulators 232 a through 232 t may be transmittedvia T antennas 234 a through 234 t, respectively.

At UE 120, antennas 252 a through 252 r may receive the downlink signalsfrom base station 110 and/or other base stations and may providereceived signals to demodulators (DEMODs) 254 a through 254 r,respectively. Each demodulator 254 may condition (e.g., filter, amplify,downconvert, and digitize) its received signal to obtain input samples.Each demodulator 254 may further process the input samples (e.g., forOFDM, etc.) to obtain received symbols. A MIMO detector 256 may obtainreceived symbols from all R demodulators 254 a through 254 r, performMIMO detection on the received symbols if applicable, and providedetected symbols. A receive processor 258 may process (e.g., demodulateand decode) the detected symbols, provide decoded data for UE 120 to adata sink 260, and provide decoded control information and systeminformation to a controller/processor 280. A channel processor maydetermine reference signal received power (RSRP), received signalstrength indicator (RSSI), reference signal received quality (RSRQ),CQI, etc.

On the uplink, at UE 120, a transmit processor 264 may receive andprocess data from a data source 262 and control information (e.g., forreports comprising RSRP, RSSI, RSRQ, CQI, etc.) fromcontroller/processor 280. Processor 264 may also generate referencesymbols for one or more reference signals. The symbols from transmitprocessor 264 may be precoded by a TX MIMO processor 266 if applicable,further processed by modulators 254 a through 254 r (e.g., for SC-FDM,OFDM, etc.), and transmitted to base station 110. At base station 110,the uplink signals from UE 120 and other UEs may be received by antennas234, processed by demodulators 232, detected by a MIMO detector 236 ifapplicable, and further processed by a receive processor 238 to obtaindecoded data and control information sent by UE 120. Processor 238 mayprovide the decoded data to a data sink 239 and the decoded controlinformation to controller/processor 240. Base station 110 may includecommunication unit 244 and communicate to network controller 130 viacommunication unit 244. Network controller 130 may include communicationunit 294, controller/processor 290, and memory 292.

Controllers/processors 240 and 280 may direct the operation at basestation 110 and UE 120, respectively. Processor 240 and/or otherprocessors and modules at base station 110, and/or processor 280 and/orother processors and modules at UE 120, may perform or direct processesfor the techniques described herein. Memories 242 and 282 may store dataand program codes for base station 110 and UE 120, respectively. Ascheduler 246 may schedule UEs for data transmission on the downlinkand/or uplink.

When transmitting data to the UE 120, the base station 110 may beconfigured to determine a bundling size based at least in part on a dataallocation size and precode data in bundled contiguous resource blocksof the determined bundling size, wherein resource blocks in each bundlemay be precoded with a common precoding matrix. That is, referencesignals (RSs) such as UE-RS and/or data in the resource blocks may beprecoded using the same precoder. The power level used for the UE-RS ineach resource block (RB) of the bundled RBs may also be the same.

The UE 120 may be configured to perform complementary processing todecode data transmitted from the base station 110. For example, the UE120 may be configured to determine a bundling size based on a dataallocation size of received data transmitted from a base station inbundles of contiguous RBs, wherein at least one reference signal inresource blocks in each bundle are precoded with a common precodingmatrix, estimate at least one precoded channel based on the determinedbundling size and one or more RSs transmitted from the base station, anddecode the received bundles using the estimated precoded channel.

FIG. 3 shows an exemplary frame structure 300 for FDD in LTE. Thetransmission timeline for each of the downlink and uplink may bepartitioned into units of radio frames. Each radio frame may have apredetermined duration (e.g., 10 milliseconds (ms)) and may bepartitioned into 10 subframes with indices of 0 through 9. Each subframemay include two slots. Each radio frame may thus include 20 slots withindices of 0 through 19. Each slot may include L symbol periods, e.g.,seven symbol periods for a normal cyclic prefix (as shown in FIG. 2) orsix symbol periods for an extended cyclic prefix. The 2L symbol periodsin each subframe may be assigned indices of 0 through 2L−1.

In LTE, an eNB may transmit a primary synchronization signal (PSS) and asecondary synchronization signal (SSS) on the downlink in the center1.08 MHz of the system bandwidth for each cell supported by the eNB. ThePSS and SSS may be transmitted in symbol periods 6 and 5, respectively,in subframes 0 and 5 of each radio frame with the normal cyclic prefix,as shown in FIG. 3. The PSS and SSS may be used by UEs for cell searchand acquisition. The eNB may transmit a cell-specific reference signal(CRS) across the system bandwidth for each cell supported by the eNB.The CRS may be transmitted in certain symbol periods of each subframeand may be used by the UEs to perform channel estimation, channelquality measurement, and/or other functions. The eNB may also transmit aphysical broadcast channel (PBCH) in symbol periods 0 to 3 in slot 1 ofcertain radio frames. The PBCH may carry some system information. TheeNB may transmit other system information such as system informationblocks (SIBs) on a physical downlink shared channel (PDSCH) in certainsubframes. The eNB may transmit control information/data on a physicaldownlink control channel (PDCCH) in the first B symbol periods of asubframe, where B may be configurable for each subframe. The eNB maytransmit traffic data and/or other data on the PDSCH in the remainingsymbol periods of each subframe.

The PSS, SSS, CRS, and PBCH in LTE are described in 3GPP TS 36.211,entitled “Evolved Universal Terrestrial Radio Access (E-UTRA); PhysicalChannels and Modulation,” which is publicly available.

FIG. 4 shows two example subframe formats 410 and 420 for the downlinkwith a normal cyclic prefix. The available time frequency resources forthe downlink may be partitioned into resource blocks. Each resourceblock may cover 12 subcarriers in one slot and may include a number ofresource elements. Each resource element may cover one subcarrier in onesymbol period and may be used to send one modulation symbol, which maybe a real or complex value.

Subframe format 410 may be used for an eNB equipped with two antennas. ACRS may be transmitted from antennas 0 and 1 in symbol periods 0, 4, 7,and 11. A reference signal is a signal that is known a priori by atransmitter and a receiver and may also be referred to as pilot. A CRSis a reference signal that is specific for a cell, e.g., generated basedon a cell identity (ID). In FIG. 4, for a given resource element withlabel Ra, a modulation symbol may be transmitted on that resourceelement from antenna a, and no modulation symbols may be transmitted onthat resource element from other antennas. Subframe format 420 may beused for an eNB equipped with four antennas. A CRS may be transmittedfrom antennas 0 and 1 in symbol periods 0, 4, 7, and 11 and fromantennas 2 and 3 in symbol periods 1 and 8. For both subframe formats410 and 420, a CRS may be transmitted on evenly spaced subcarriers,which may be determined based on cell ID. Different eNBs may transmittheir CRSs on the same or different subcarriers, depending on their cellIDs. For both subframe formats 410 and 420, resource elements not usedfor the CRS may be used to transmit data (e.g., traffic data, controldata, and/or other data).

An interlace structure may be used for each of the downlink and uplinkfor FDD in LTE. For example, Q interlaces with indices of 0 through Q−1may be defined, where Q may be equal to 4, 6, 8, 10, or some othervalue. Each interlace may include subframes that are spaced apart by Qframes. In particular, interlace q may include subframes q, q+Q, q+2Q,etc., where qε{0, . . . , Q−1}.

The wireless network may support hybrid automatic retransmission request(HARQ) for data transmission on the downlink and uplink. For HARQ, atransmitter (e.g., an eNB 110) may send one or more transmissions of apacket until the packet is decoded correctly by a receiver (e.g., a UE120) or some other termination condition is encountered. For synchronousHARQ, all transmissions of the packet may be sent in subframes of asingle interlace. For asynchronous HARQ, each transmission of the packetmay be sent in any subframe.

A UE may be located within the coverage of multiple eNBs. One of theseeNBs may be selected to serve the UE. The serving eNB may be selectedbased on various criteria such as received signal strength, receivedsignal quality, path loss, etc. Received signal quality may bequantified by a signal-to-interference-plus-noise ratio (SINR), or areference signal received quality (RSRQ), or some other metric. The UEmay operate in a dominant interference scenario in which the UE mayobserve high interference from one or more interfering eNBs.

Downlink Coverage Issues

According to certain wireless communication systems (e.g., in LTERel-8/9/10), PDCCH is located in the first few symbols in a subframe.With these systems, PDCCH may be fully distributed in the entire systembandwidth. In addition, PDCCH may be time-division multiplexed (TDM'd)with PDSCH. In this manner, a subframe is effectively divided into acontrol region and a data region

In certain systems, a new control channel (e.g., enhanced PDCCH orePDCCH) may be introduced. Unlike a conventional or “legacy” PDCCH,which occupies the first several control symbols in a subframe, ePDCCHmay occupy the data region, similar to PDSCH. ePDCCH may increasecontrol channel capacity, support frequency-domain inter-cellinterference coordination (ICIC), achieve improved spatial reuse ofcontrol channel resources, support beamforming and/or diversity, operateon the new carrier type (NCT) and in Multimedia Broadcast SingleFrequency Network (MBSFN) subframes, and coexist on the same carrier aslegacy UEs.

One of the main focuses of traditional LTE design is on the improvementof spectral efficiency, ubiquitous coverage, enhanced Quality of Service(QoS) support, and the like. This typically results in high-end devices,such as state-of-art smartphones, tablets, and other such devices.

However, it may also be desirable to support low cost, low data ratedevices (e.g., in accordance with LTE Rel-11), as well. Some marketprojections show that the number of low cost devices may largely exceedtoday's cell phones. Various design aspects may be employed to designsuch low cost, low rate devices, such as reduction of maximum bandwidth,use of a single receive radio frequency (RF) chain, reduction of peakrate, reduction of transmit power, and half duplex operation.

In general, since the intended data rate for the low cost device may besignificantly lower than conventional devices (e.g., less than 100kbps), it is possible to operate the low cost device only at narrowbandwidth to reduce the cost. There are generally two operationscenarios under consideration. One straightforward deployment scenariois to set aside some narrow bandwidth (e.g. 1.25 MHz) to support themachine type communications (MTC) operations. No standard changes areinvolved for such operations.

A second, possibly more interesting deployment scenario may be tooperate low cost UEs in a large bandwidth, such that low cost UEs maycoexist with regular UEs. There are at least two possible operations forlow cost UEs in a large bandwidth. First, low cost UEs may still operatewith the same large bandwidth (e.g., up to 20 MHz) as regular UEs. Thisneed not involve change to existing standards, but may not be helpful inreducing cost and battery power consumption. Second, low cost UEs mayoperate with a smaller bandwidth (within a larger bandwidth).

In certain systems (e.g., LTE Rel-8/9/10), transmission time interval(TTI) or subframe bundling may be configured on a per-UE basis. Thesubframe bundling operation may be configured, for example, by theparameter “ttiBundling” provided by higher layers. If TTI bundling isconfigured for a UE, the subframe bundling operation may only be appliedto the Uplink Shared Channel (UL-SCH) (and not be applied to other ULsignals/traffic, such as uplink control information). The bundling sizemay be fixed (e.g., at 4 subframes). That is, the Physical Uplink SharedChannel (PUSCH) may be transmitted in 4 consecutive subframes, and thesame hybrid automatic repeat request (HARQ) process number may be usedin each of the bundled subframes. The resource allocation size may berestricted (e.g., to up to 3 RBs) and the modulation order may be fixed(e.g., set to 2 with quadrature phase-shift keying (QPSK)). A bundle maybe treated as a single resource (e.g., a single grant and a single HARQacknowledgement (ACK) may be used for each bundle).

While TTI bundling is used mainly for low rate traffic, there are othermotives for implementing TTI bundling. Although segmentation is onealternative to TTI bundling, there are disadvantages. For example, ifvoice over Internet protocol (VoIP) packets cannot be transmitted in asingle TTI due to a low UL link budget, Layer 2 (L2) segmentation may beapplied. For example, a VoIP packet may be segmented in 4 radio linkcontrol (RLC) protocol data units (PDUs) that are transmitted in 4consecutive TTIs and 2-3 HARQ retransmissions might be targeted toachieve sufficient coverage. This approach has various drawbacks. Forexample, each additional segment introduces a 1 byte RLC, a 1 byte mediaaccess control (MAC), and a 3 byte Layer 1 (L1) cyclic redundancy check(CRC) overhead (i.e., 15% overhead assuming a 33 byte RLC service dataunit (SDU) size). This means that for 4 segments, there is an additionalL1/L2 overhead of 45%. HARQ transmissions/retransmissions for everysegment may entail grants on PDCCH, consuming significant PDCCHresources. Each HARQ transmission or retransmission is followed by HARQfeedback on the Physical HARQ Indicator Channel (PHICH). Assuming anegative ACK (NACK)-to-ACK error ratio of 10⁻³, the large number of HARQfeedback signals leads to high packet loss probabilities. For example,if 12 HARQ feedback signals are sent, the HARQ feedback error ratiomight be on the order of 1.2*10⁻². Packet loss rates of more than 10⁻²are generally unacceptable for VoIP traffic.

Furthermore, usage of only a single uplink grant and a single PHICHsignal per TTI bundle may be advantageous. Also, the L1 and L2 overheadmay be minimized since L2 segmentation need not be applied.

TTI bundling may also prove useful for UL coverage enhancements. Forexample, it may be desirable to increase coverage for medium data ratePUSCH and UL VoIP. The minimum gain for consideration of specifying thepotential solution is 1 dB for both medium data rate PUSCH and UL VoIP.Potential solutions include TTI bundling enhancements for medium datarate and VoIP. For this solution, both L1 (and higher layers') protocolsoverhead and latency may be considered.

Example Downlink Coverage Enhancements

Various issues exist with DL coverage for low cost devices. For example,low cost UEs may have only 1 receive (Rx) antenna, thereby impacting DLcoverage. DL coverage enhancements may also be desirable because atransmitting cell may use reduced transmission power (e.g., to reduceinterference with other cells).

In LTE Rel-8, at least for large system bandwidths, a base station (eNB)may have the flexibility of using power control and/or resource controlto manage DL coverage for a UE. A control channel for a coverage-limitedUE may use a large aggregation level and can further be power boosted(potentially with some limitation), especially when there are very fewsimultaneous control channels transmissions in a given subframe. A datachannel for a UE may have a low coding rate and can be power boosted(potentially with some limitation), as well, especially when PDSCH isnarrowband and there are very few simultaneous data transmissions in agiven subframe.

Since coverage is typically UL limited, there may be no strong desire insome cases (e.g., LTE Rel-8) to standardize any DL coverageenhancements. However, in the future (e.g., in LTE Rel-12), DL coverageimprovements may be much more desired. In such cases, a UE may have only1 receive chain (versus 2), which may result in at least a 3 dB loss. AUE may also have narrowband operation, resulting in frequency diversitygain loss, limited power boosting possibility, and limited lowestpossible coding rate.

Techniques presented herein, however, may provide for possible DLcoverage enhancements. Such DL coverage enhancements may be made fortransmitting downlink control channels (e.g., via reduced payload size,increased number of resources per subframe, TTI bundling over differentsubframes, and/or beamforming) and for transmitting downlink datachannels (e.g., beamforming and/or TTI bundling over differentsubframes).

As outlined above, DL coverage enhancements may be utilized fortransmitting various control channels. Such control channels includePBCH, Physical Control Format Indicator Channel (PCFICH) (or enhancedePCFICH), PHICH (or enhanced ePHICH), PDCCH (or enhanced ePDCCH). ForPBCH, coverage may be enhanced by reducing PBCH payload size (e.g., froma current 24 bits including 9 reserved bits, to a smaller number ofbits).

For PCFICH or ePCFICH, DL coverage may be enhanced by increasing thenumber of resources such that the coding rate is reduced (e.g.,increasing from 16 resource elements (REs) to 32 REs via simplerepetition). A cell may support one or more (e)PCFICH configurationstargeting different coverage and may indicate which one to use in asubframe. In some cases, there may be no support of dynamic controlupdate (e.g., reducing/eliminating the desire for (e)PCFICH).

For PHICH or ePHICH, DL coverage may be enhanced by increasing thenumber of resources such that the coding rate is reduced (e.g.,increased from 12 REs to 24 REs via simple repetition). A cell maysupport one or more (e)PHICH configurations targeting different coverageand may indicate (via signaling) which configuration to use in asubframe. In some cases, there may be no (e)PHICH-based UL HARQoperation.

For PDCCH and ePDCCH, DL coverage may be enhanced by payload sizereduction. For example, more compact Downlink Control Information (DCI)formats may be introduced. It may be noted that the extent of payloadsize reduction may be different for broadcast and unicast control (e.g.,the payload size reduction for broadcast may be less than the payloadsize reduction for unicast). In particular, a DCI scheduling broadcastmay not be the same size as a DCI scheduling unicast, as in the Rel-8case (DCI format 1A has the same size for broadcast and unicast in thecommon search space).

DL coverage for (e)PDCCH may also be enhanced by increasing resources.For example, for regular UEs, aggregation levels 1/2/4/8 are supportedfor PDCCH, corresponding to 36/72/144/288 resource elements,respectively. For coverage-limited UEs, a different set of aggregationlevels for (e)PDCCH (e.g., 2/4/8/16) may be considered. However, thisoption may not be possible if the system bandwidth is small (e.g., 6RBs), at least for PDCCH.

Coverage may also be enhanced by utilizing TTI bundling. For example, asingle DCI may be transmitted over multiple subframes. The PDCCHcarrying the same DCI in different subframes of the same bundle may usethe same aggregation level. While it may be possible to have differentlevels (e.g., by radio resource control (RRC) configuration, orpotentially combined with, say, subframe id_(x)), it may not bepreferable due to complexity. The PDCCH in each subframe (of the bundle)may be individually coded, modulated, and mapped to resources, insteadof jointly performed. It may be desirable, in some cases, to use thesame modulation/coding rate (e.g., repetition over the subframes in thebundle). The Control Channel Element(s) (CCE(s)) in each subframe neednot be the same, but it may be desirable that the CCE(s) be implicitlylinked. For example, the same decoding candidate index may be used inthe UE-specific search space, although the UE-specific search space canbe subframe dependent.

In some cases, aggregation levels may be different in differentsubframes in the same bundle depending on resource availability. Forexample, the available resources for PDCCH or ePDCCH (based on subframetype, and/or indicated by PCFICH or ePCFICH) may be limited, and a UEstarts with level 8 PDCCH or ePDCCH in a first subframe and may uselevel 4 in a second subframe in the same bundle if the second subframehas a resource availability limitation.

In some cases, a UE may perform early decoding when TTI bundling is usedfor DL coverage enhancement. For example, if a UE successfully decodes aPDCCH/ePDCCH/PDSCH before the last subframe in the bundle, the UE mayskip decoding for the rest of subframes in the bundle (which may reducepower consumption at the UE).

It may be desirable not to increase the number of blind decodes whenutilizing TTI bundling. For example, it may be possible to maintain thesame number of blind decodes per subframe by having the UE monitor thesame aggregation level and the same decoding candidate of theaggregation level over the subframes in the bundle for a DCI.

As an example, {L, k} may be used to indicate a combination ofaggregation level L and a decoding candidate k. Suppose there areaggregation levels {1, 2, 4 8} with {6, 6, 2, 2} decoding candidates,respectively, as in Rel-8 for PDCCH. For this example, the bundling sizeN may be assumed to be N=2. Then, the decoding candidates for a UE are{1, 1}, {1, 2}, . . . , {1, 6}, {2, 1}, {2, 2}, . . . , {2, 6}, {4, 1},{4, 2}, {8, 1}, {8, 2} for all subframes in the bundle. In other words,for a particular DCI, if it is transmitted using {8, 1} in the firstsubframe in a bundle, the same {8, 1} would be used in all the remainingsubframes in the same bundle.

Additional flexibility may also be possible (e.g., via some implicitderivation), but eNB and UE should be aligned.

When utilizing TTI bundling, it may be desirable for a UE to know a“subframe offset,” which indicates the subframe corresponding to astarting subframe in the bundle. In some cases, the starting subframefor a control channel in bundling can be hard-coded, semi-staticallydetermined, or dynamically determined. Different control channeldecoding candidates may have different subframe offset determinationschemes. For example, the common search space may have a hard-codedscheme, while the UE-specific search space may have a semi-staticscheme.

As outlined above, hard-coded subframe offsets may be utilized. Forexample, if the bundling size is 2, it can be specified that thebundling operation always starts from an even subframe for a cell. Itmay be further enhanced to have a cell-dependent offset (e.g., linkedwith the cell ID). As an example, based on cell ID, a cell may bedetermined to have even subframe offsets, while another cell may bedetermined to have odd subframe offsets. Semi-static subframe offsetsmay also be utilized, for example, via RRC configuration. Dynamicoffsets may be, for example, indicated by other channels, linked withthe frame index, blindly detected by the UE, or by some other mechanism.

A UE may most likely also be made aware of the TTI bundling size. Thenumber of subframes can be fixed (e.g., 4), configurable (e.g., viaRRC), or dynamic. Rate matching, scrambling, interleaving, and othersuch physical layer operations may be the same for the subframes in thesame bundle, especially when the bundling size is dynamicallydetermined. Alternatively, rate matching, scrambling, interleaving, orsome other physical layer operations may be different for differentsubframes in the same bundle, especially when the bundling size is fixedor semi-statically configured.

UE decoding of the control channel with TTI bundling may vary dependingon bundling parameters. The UE can perform control channel decodingevery N (bundling size) subframes, especially when the subframe offsetand/or bundling size is fixed or semi-statically determined.Alternatively, the UE may perform decoding of the control channel everysingle subframe, especially when the subframe offset and/or bundlingsize is dynamically determined. In some cases, the UE may try to firstdecode the current subframe and then to soft combine the currentsubframe with the previous one, etc. The UE may directly store the softdetection symbols (e.g., log-likelihood ratio, or LLR) from the previoussubframe for redundancy combining. If the UE does not know the bundlingsize, it may not know the HARQ timing. To address this issue, the UE maybe notified of the HARQ timing in the grants. As an example, if thebundle size is 2 subframes, one bit in the grant may be included toindicate whether the last subframe in a bundle is an even- orodd-numbered subframe. For blind decoding of the subframe offset and/orsize for bundling, there may be ambiguity regarding the offset betweenthe eNB and UE (e.g., a UE may determine an incorrect offset). This maybe alleviated by modifying the control channel design (e.g., offsetdependent rate matching, scrambling, interleaving, etc.) as discussedabove.

In some cases, DL coverage may be enhanced by additional beamforminggain for a localized ePDCCH. More transmit (Tx) antennas (e.g., greaterthan 8) may also be considered. The same precoding for the ePDCCHs indifferent subframes of the same bundle may be used in an effort toimprove ePDCCH channel estimation and decoding performance.

Different control channel decoding candidates may adopt different DLcoverage enhancement techniques. For example, common search spacecontrol channel transmissions may rely on TTI bundling, distributedePDCCH may also rely on TTI bundling, but localized ePDCCH may rely onbeamforming.

Various techniques (described above and further described below) forenhancing DL coverage may also be applied for transmitting datachannels.

In some cases, the PDSCH may be transmitted utilizing transmitdiversity. Such transmissions may be broadcast or unicast. TTI bundlingmay be utilized when transmitting DL data. A single transport block (TB)may be transmitted over multiple subframes. The number of subframes maybe fixed (e.g., 4), configurable (e.g., via RRC), or dynamicallyindicated via a control channel. The PDSCH in each subframe for the sameTB may be individually coded, modulated, and mapped to resources,instead of jointly performed. For certain aspects, the same modulationand coding scheme (MCS) is used for the PDSCH in all the subframes ofthe same bundle (e.g., a simple repetition over different subframes).For other aspects, different MCSs may be used for the PDSCH in allsubframes of the same bundle, where the various MCSs in differentsubframes of the same bundle are linked with each other. In other words,a UE may be informed of the MCS scheme for the first subframe of thebundle, and the UE may determine the MCSs for the remaining subframes ofthe bundle based on the MCS for the first subframe.

In some cases, the PDSCH carrying the same TB in different subframes mayuse the same amount of RBs, but the locations of the RBs need not be thesame. This may depend on resource allocation types, whether hopping isenabled or not, and the like. However, for certain aspects, thelocations of the RBs in the second and onward subframes may beimplicitly derived based on the locations of the RBs in the firstsubframe of the same bundle.

Additional beamforming gain may also be utilized to enhance DL coveragefor the PDSCH, for example. For certain aspects, the same precoding forthe PDSCHs in the same bundle may be used in an effort to improve PDSCHchannel estimation and decoding performance.

As described above for control channels, the subframe offset for PDSCHin bundling may be hard-coded, semi-statically determined, ordynamically determined. For example, different PDSCHs may have differentsubframe offset determination schemes (e.g., broadcast versus unicast).

In some cases, DL HARQ operation under TTI bundling may be adjusted forenhanced DL coverage. Scheduling timing (from (e)PDCCH to PDSCH) may beas with regular UEs: in the same subframe. For same subframe scheduling,the number of bundled subframes for control may be the same or less thanthat for data. This may be simple, but a UE would have to buffer fordata before control can be decoded. As an alternative, cross-subframescheduling may be utilized (i.e., different subframes for control anddata), which may relax buffering implications at the UE. As an example,a control channel may be transmitted in subframe n, while thecorresponding data channel is transmitted in subframes n+1, n+2, n+3 andn+4.

In some cases, HARQ ACK timing (from PDSCH to ACK/NAK) may be adjustedfor enhanced DL coverage. For regular UEs, the HARQ ACK timing can be 4ms in FDD, and ≧4 ms in TDD. For coverage-limited UEs, the HARQ ACK/NAKtiming may be linked with PDSCH of the last subframe in the bundle,regardless of whether PDSCH is transmitted in the last subframe or not(PDSCH may not be transmitted in some subframes, as described below).The timing may be the same as for regular UEs or may be relaxed (>4 ms).

The number of HARQ processes may also be adjusted, for example,depending on the bundling size, scheduling timing, and HARQ ACK timing.As an example, the number of HARQ processes may be determined byfloor((scheduling delay+HARQ ACK delay)/bundling)+1. If scheduling delayis zero (i.e., same subframe scheduling) and HARQ ACK delay is 4 ms (forbundling size of 4), there may be up to 2 DL HARQ processes for the UE.

As an alternative, HARQ-less operation for bundled PDSCH transmissionsmay also be considered.

UL HARQ operation may also be considered under TTI bundling. Thescheduling timing ((e)PDCCH to PUSCH) can be defined based on the lastcontrol subframe in the bundle to the first PUSCH subframe, regardlessof whether the last control subframe transmits the control channel ornot. The HARQ ACK timing (PUSCH to (e)PHICH and (e)PDCCH) can be definedbased on the PUSCH subframe to the first control subframe in the bundle.The number of UL HARQ processes may also be reduced due to increased ULround-trip time (RTT) compared with the non-bundling case.

The interaction between control and data may also be considered whenenhancing DL coverage. For example, DL TTI bundling may be enabled forcontrol only, data only, or both. As an example, TTI bundling may beutilized for data only, but not for control. Instead, a differentcoverage enhancement technique can be adopted for a control channel,e.g., by increasing the number of resources used by the control channel.This approach is favorable, especially given the impact on UL HARQoperation.

The interaction with MBSFN subframes may also be considered whenenhancing DL coverage. For example, the subframes in the bundle may beconsecutive DL subframes. However, some subframes may not be availablefor PDSCH transmissions, for example, as with MBSFN subframes configuredfor multimedia broadcast and multicast service (MBMS) transmissions. Inthis case, PDSCH transmissions in these subframes can be omitted, suchthat the effective number of subframes in a bundle is reduced.Alternatively, the subframes in a bundle can be defined as consecutiveand available DL subframes. With this approach, subframes not availablefor PDSCH may be excluded from bundling to ensure the actual number ofPDSCH transmissions in a bundle is equal to the bundling size. However,this approach may complicate HARQ operation (which may lead toconsidering HARQ-less operation).

TDD-specific considerations may also be made when enhancing DL coverage.For example, TTI bundling may most likely be only over DL subframes(skipping UL subframes). Special subframes may be skipped, too, if theDwPTS length is too small to carry any PDSCH or ePDCCH. For DwPTS inspecial subframes carrying PDSCH/ePDCCH, the number of availableresources is typically less than that of regular DL subframes. Toaddress this issue, two design alternatives may be considered. In afirst alternative, the number of RBs (or resources) for PDSCH/ePDCCH inDwPTS is the same as that of the regular DL subframes in the samebundle. This may be simple, but performance may be degraded slightly. Asa second alternative, the number of RBs (or resources) for PDSCH/ePDCCHin DwPTS may be adjusted compared with that of the regular DL subframesin the same bundle. This may be a bit more complicated, but may improveperformance. In some cases, the adjustment factor can be based on thecurrent transport block size (TBS) adjustment factor or can be newlydefined. As an example, if the TBS adjustment factor is 0.75, the RBadjustment factor in DwPTS under DL TTI bundling can be ceiling(N_RB/0.75), where N_RB is the number of RBs in regular DL subframes ofthe same bundle.

FIG. 5 illustrates example operations 500 for enhanced downlinkcoverage. The operations may be performed, for example, by a basestation (e.g., an eNB 110).

The operations 500 may begin, at 502, with the base station identifyinga first type of one or more user equipments (UEs) with limited downlink(DL) coverage—or that is to receive enhanced DL coverage—relative to asecond type of UEs. At 504, the base station utilizes one or more DLcoverage enhancement techniques when communicating with the first typeof UEs, the DL coverage enhancement techniques designed to compensate(or at least adjust) at least for reduced DL processing gain of thefirst type of UEs relative to the second type of UEs. The reduced DLprocessing gain may be due to at least one of a reduced number ofreceive chains relative to the second type of UEs, reduced downlinktransmission power, or narrower bandwidth operation relative to thesecond type of UEs.

According to certain aspects, the one or more DL coverage enhancementtechniques involve reducing a payload size of one or more controlchannels when transmitting to the first type of UEs relative to apayload size of the same control channels when transmitting to thesecond type of UEs. For certain aspects, a first payload size is usedwhen transmitting a unicast message of a first type of control channel,and a second payload size is used when transmitting a non-unicastmessage of the first type of control channel.

According to certain aspects, the one or more DL coverage enhancementtechniques include increasing resources available for one or morecontrol channels to support a reduced coding rate. The increase inresources may be relative to a number of resources available whentransmitting the same control channels to the second type of UEs. Forcertain aspects, the same information is repeated in different sets ofresource elements (REs) of the increased resources. For certain aspects,the operations 500 further includes the base station receiving signalingindicating one or more subframes in which a control channel is to betransmitted using the increased resources.

According to certain aspects, the one or more DL coverage enhancementtechniques include transmission time interval (TTI) bundling, whereinredundant versions of a downlink channel are transmitted over a bundleof multiple DL subframes. For example, the bundle may include Nconsecutive DL subframes or N consecutive non-Multimedia BroadcastSingle Frequency Network (non-MBSFN) DL subframes. For certain aspects,different numbers of resource blocks (RBs) are used to transmit thedownlink channel for DL subframes in the bundle with and without adownlink pilot time slot (DwPTS). A same aggregation level may be usedfor transmitting the downlink channel in each subframe in the bundle.For other aspects, different aggregation levels may be used fortransmitting the downlink channel in different subframes in the bundle.The aggregation level used in a subframe may be dependent on availableresources in that subframe. For certain aspects, a version of thedownlink channel in each subframe in the bundle is individually coded,modulated, and mapped to resources. For certain aspects, different setsof control channel elements (CCEs) are used to transmit versions of thedownlink channel in different subframes, and locations of the differentsets of CCEs in the different subframes are linked. For certain aspects,a scheduling timing between a control channel and a correspondingphysical downlink shared channel (PDSCH) transmitted via the TTIbundling is determined based on a first subframe in the bundle.According to certain aspects, a hybrid automatic repeat request (HARQ)timing between a physical downlink shared channel (PDSCH) transmittedvia the TTI bundling and a corresponding HARQ response is determinedbased on a last subframe in the bundle. A number of hybrid automaticrepeat request (HARQ) processes supported may be dependent on a TTIbundling size. For certain aspects, a same decoding candidate is usedfor transmitting the downlink channel in each subframe in the bundle.

The downlink channel may be a physical downlink shared channel (PDSCH).According to certain aspects, the TTI bundling involves transmitting asingle transport block (TB) over multiple subframes. For certainaspects, the TB is transmitted in each subframe of the bundle using asame modulation and coding scheme (MCS). For certain aspects, the TB istransmitted in each subframe of the bundle using a same number ofresource blocks (RBs). The TB may be transmitted in each subframe of thebundle using different locations of resource blocks (RBs).

According to certain aspects, a subframe offset for a starting subframein the bundle is determined at least one of semi-statically ordynamically. The subframe offset for the starting subframe in the bundlemay be cell-dependent.

For certain aspects, a size of the bundle is at least one of fixed orsemi-statically configured. One or more physical layer (PHY) operationsfor transmitting a version of the downlink channel may vary in differentsubframes in the bundle. For other aspects, a size of the bundle isdynamically configured. One or more physical layer (PHY) operations fortransmitting a version of the downlink channel may be the same indifferent subframes in the bundle.

According to certain aspects, utilizing the one or more DL coverageenhancement techniques at 504 includes utilizing a first technique for acontrol channel and utilizing a second technique for a data channel forthe first type of UEs.

For certain aspects, cross-subframe scheduling is utilized, such that acontrol channel sent in a first subframe schedules a data transmissionin a subsequent subframe.

According to certain aspects, the one or more DL coverage enhancementtechniques include utilizing additional beamforming gain.

According to certain aspects, different DL coverage enhancementtechniques are used for DL channels transmitted in different decodingcandidates.

FIG. 6 illustrates example operations 600 for enhanced downlinkcoverage. The operations may be performed, for example, by a UE 120.

The operations 600 may begin, at 602, with the UE, which is of a firsttype of UEs with limited DL coverage—or that is to receive enhanced DLcoverage—relative to a second type of UEs, receiving informationregarding one or more DL coverage enhancement techniques utilized by abase station when communicating with the UE to compensate (or at leastadjust) at least for reduced DL processing gain of the first type of UEsrelative to the second type of UEs. For certain aspects, the reduced DLprocessing gain is due to at least one of a reduced number of receivechains relative to the second type of UEs, reduced downlink transmissionpower, or narrower bandwidth operation relative to the second type ofUEs.

At 604, the UE receives one or more downlink transmissions from the basestation, transmitted utilizing the one or more DL coverage enhancementtechniques. At 606, the UE may process the one or more downlinktransmissions based on the received information.

According to certain aspects, the one or more DL coverage enhancementtechniques include reducing a payload size of one or more controlchannels when transmitting to the first type of UEs relative to apayload size of the same control channels when transmitting to thesecond type of UEs. For certain aspects, a first payload size is usedwhen transmitting a unicast message of a first type of control channel,and a second payload size is used when transmitting a non-unicastmessage of the first type of control channel.

According to certain aspects, the one or more DL coverage enhancementtechniques include increasing resources available for one or morecontrol channels to support a reduced coding rate. For certain aspects,the increase in resources is relative to a number of resources availablewhen transmitting the same control channels to the second type of UEs.For certain aspects, the same information is repeated in different setsof REs of the increased resources.

According to certain aspects, the one or more DL coverage enhancementtechniques include TTI bundling, wherein the one or more downlinktransmissions include redundant versions of a downlink channeltransmitted over a bundle of multiple DL subframes. The bundle maycomprise N consecutive DL subframes or N consecutive non-MBSFN DLsubframes, for example. For certain aspects, different numbers of RBsare used to transmit the downlink channel for DL subframes in the bundlewith and without a DwPTS. The downlink channel may be transmitted usinga same aggregation level in each subframe in the bundle or usingdifferent aggregation levels in different subframes in the bundle. Inthe latter case, the aggregation level used in a subframe may bedependent on available resources in that subframe. For certain aspects,a version of the downlink channel in each subframe in the bundle isindividually coded, modulated, and mapped to resources. For certainaspects, different sets of CCEs may be used to transmit versions of thedownlink channel in different subframes, and locations of the differentsets of CCEs in the different subframes may be linked.

According to certain aspects, the downlink channel is a PDSCH. In thiscase, the TTI bundling may involve transmitting a single TB overmultiple subframes. For certain aspects, the TB is transmitted in eachsubframe of the bundle using at least one of a same MCS, a same numberof RBs, or different locations of the RBs.

For certain aspects, a scheduling timing between a control channel and acorresponding PDSCH transmitted via the TTI bundling is determined basedon a first subframe in the bundle. For certain aspects, a HARQ timingbetween a PDSCH transmitted via the TTI bundling and a correspondingHARQ response is determined based on a last subframe in the bundle. Forcertain aspects, a number of HARQ processes supported is dependent on aTTI bundling size. According to certain aspects, if the UE successfullydecodes the downlink channel before the last subframe in the bundle, theUE may skip decoding the downlink channel for remaining subframes in thebundle. For certain aspects, a same decoding candidate is used fortransmitting the downlink channel in each subframe in the bundle. A sizeof the bundle may be at least one of fixed or semi-staticallyconfigured. For certain aspects, one or more physical layer (PHY)operations for transmitting a version of the downlink channel vary indifferent subframes in the bundle. The size of the bundle may bedynamically configured. For certain aspects, one or more PHY operationsfor transmitting a version of the downlink channel are the same indifferent subframes in the bundle.

According to certain aspects, a subframe offset for a starting subframein the bundle is determined at least one of semi-statically ordynamically. The subframe offset for the starting subframe in the bundlemay be cell-dependent.

According to certain aspects, the one or more DL coverage enhancementtechniques include utilizing a first technique for a control channel andutilizing a second technique for a data channel for the first type ofUEs.

According to certain aspects, cross-subframe scheduling is utilized,such that a control channel sent in a first subframe schedules a datatransmission in a subsequent subframe.

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software/firmwarecomponent(s) and/or module(s), including, but not limited to a circuit,an application specific integrated circuit (ASIC), or processor.Generally, where there are operations illustrated in the Figures, thoseoperations may be performed by any suitable corresponding counterpartmeans-plus-function components.

For example, means for transmitting may comprise a transmitter (e.g., amodulator 232) and/or an antenna 234 of the eNB 110 illustrated in FIG.2. Means for receiving may comprise a receiver (e.g., a demodulator 232)and/or an antenna 234 of the eNB 110 illustrated in FIG. 2. Means forprocessing, means for utilizing one or more DL coverage enhancementtechniques, means for identifying, or means for determining may comprisea processing system, which may include at least one processor, such asthe receive processor 238, the controller/processor 240, and/or thetransmit processor 220 of the eNB 110 illustrated in FIG. 2. However,additional or alternative components in FIG. 2 may be employed as thevarious means described above.

It is understood that the specific order or hierarchy of steps in theprocesses disclosed is an example of exemplary approaches. Based upondesign preferences, it is understood that the specific order orhierarchy of steps in the processes may be rearranged while remainingwithin the scope of the present disclosure. The accompanying methodclaims present elements of the various steps in a sample order, and arenot meant to be limited to the specific order or hierarchy presented.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or combinations thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the disclosure herein may be implemented as electronichardware, software/firmware, or combinations thereof. To clearlyillustrate this interchangeability of hardware and software, variousillustrative components, blocks, modules, circuits, and steps have beendescribed above generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software/firmware dependsupon the particular application and design constraints imposed on theoverall system. Skilled artisans may implement the describedfunctionality in varying ways for each particular application, but suchimplementation decisions should not be interpreted as causing adeparture from the scope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the disclosure herein may be implemented or performedwith a general-purpose processor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device (PLD), discretegate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thedisclosure herein may be embodied directly in hardware, in asoftware/firmware module executed by a processor, or in a combinationthereof. A software/firmware module may reside in RAM memory, flashmemory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, aremovable disk, a CD-ROM, or any other form of storage medium known inthe art. An exemplary storage medium is coupled to the processor suchthat the processor can read information from, and write information to,the storage medium. In the alternative, the storage medium may beintegral to the processor. The processor and the storage medium mayreside in an ASIC. The ASIC may reside in a user terminal. In thealternative, the processor and the storage medium may reside as discretecomponents in a user terminal.

In one or more exemplary designs, the functions described may beimplemented in hardware, software/firmware, or combinations thereof. Ifimplemented in software, the functions may be stored on or transmittedover as one or more instructions or code on a computer-readable medium.Computer-readable media include both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. A storage medium may be anyavailable medium that can be accessed by a general purpose or specialpurpose computer. By way of example, and not limitation, suchcomputer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other medium that can be used to carry or store desiredprogram code means in the form of instructions or data structures andthat can be accessed by a general-purpose or special-purpose computer,or a general-purpose or special-purpose processor. Also, any connectionis properly termed a computer-readable medium. For example, if thesoftware is transmitted from a website, server, or other remote sourceusing a coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared, radio,and microwave, then the coaxial cable, fiber optic cable, twisted pair,DSL, or wireless technologies such as infrared, radio, and microwave areincluded in the definition of medium. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and Blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Thus, in some aspects computer-readable media may comprisenon-transitory computer-readable media (e.g., tangible media). Inaddition, for other aspects computer-readable media may comprisetransitory computer-readable media (e.g., a signal). Combinations of theabove should also be included within the scope of computer-readablemedia.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of a, b, or c” is intended to cover a, b, c,a-b, a-c, b-c, and a-b-c.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples and designs described herein but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

What is claimed is:
 1. A method for wireless communications by a basestation, comprising: identifying a first type of one or more userequipments (UEs) that is to receive enhanced downlink (DL) coveragerelative to a second type of UEs; and utilizing one or more DL coverageenhancement techniques when communicating with the first type of UEs,the one or more DL coverage enhancement techniques designed to adjust atleast for reduced DL processing gain of the first type of UEs relativeto the second type of UEs.
 2. The method of claim 1, wherein the reducedDL processing gain is due to at least one of: a reduced number ofreceive chains relative to the second type of UEs; reduced downlinktransmission power; or narrower bandwidth operation relative to thesecond type of UEs.
 3. The method of claim 1, wherein the one or more DLcoverage enhancement techniques comprise reducing a payload size of oneor more control channels when transmitting to the first type of UEsrelative to a payload size of the same control channels whentransmitting to the second type of UEs.
 4. The method of claim 3,wherein: a first payload size is used when transmitting a unicastmessage of a first type of control channel; and a second payload size isused when transmitting a non-unicast message of the first type ofcontrol channel.
 5. The method of claim 1, wherein the one or more DLcoverage enhancement techniques comprise increasing resources availablefor one or more control channels to support a reduced coding rate. 6.The method of claim 5, wherein the increase in resources is relative toa number of resources available when transmitting the same controlchannels to the second type of UEs.
 7. The method of claim 5, whereinthe same information is repeated in different sets of resource elements(REs) of the increased resources.
 8. The method of claim 5, furthercomprising receiving signaling indicating one or more subframes in whicha control channel is to be transmitted using the increased resources. 9.The method of claim 1, wherein the one or more DL coverage enhancementtechniques comprise transmission time interval (TTI) bundling whereinredundant versions of a downlink channel are transmitted over a bundleof multiple DL subframes.
 10. The method of claim 9, wherein the bundlecomprises N consecutive DL subframes.
 11. The method of claim 9, whereinthe bundle comprises N consecutive non-Multimedia Broadcast SingleFrequency Network (non-MBSFN) DL subframes.
 12. The method of claim 9,wherein different numbers of resource blocks (RBs) are used to transmitthe downlink channel for DL subframes in the bundle with and without adownlink pilot time slot (DwPTS).
 13. The method of claim 9, wherein thedownlink channel comprises a physical downlink shared channel (PDSCH).14. The method of claim 13, wherein the TTI bundling comprisestransmitting a single transport block (TB) over multiple subframes. 15.The method of claim 14, wherein the TB is transmitted in each subframeof the bundle using a same modulation and coding scheme (MCS).
 16. Themethod of claim 14, wherein the TB is transmitted in each subframe ofthe bundle using a same number of resource blocks (RBs).
 17. The methodof claim 16, wherein the TB is transmitted in each subframe of thebundle using different locations of resource blocks (RBs).
 18. Themethod of claim 9, wherein a scheduling timing between a control channeland a corresponding physical downlink shared channel (PDSCH) transmittedvia the TTI bundling is determined based on a first subframe in thebundle.
 19. The method of claim 9, wherein a hybrid automatic repeatrequest (HARQ) timing between a physical downlink shared channel (PDSCH)transmitted via the TTI bundling and a corresponding HARQ response isdetermined based on a last subframe in the bundle.
 20. The method ofclaim 9, wherein a number of hybrid automatic repeat request (HARQ)processes supported is dependent on a TTI bundling size.
 21. The methodof claim 1, wherein the one or more DL coverage enhancement techniquescomprise using a same aggregation level for transmitting the downlinkchannel in each subframe in a bundle of subframes.
 22. The method ofclaim 1, wherein the one or more DL coverage enhancement techniquescomprise using different aggregation levels for transmitting thedownlink channel in different subframes in a bundle of subframes. 23.The method of claim 22, wherein an aggregation level used in a subframeis dependent on available resources in that subframe.
 24. The method ofclaim 1, wherein the one or more DL coverage enhancement techniquescomprise transmitting the downlink channel in a bundle of subframes andwherein a version of the downlink channel in each subframe in the bundleis individually coded, modulated, and mapped to resources.
 25. Themethod of claim 1, wherein the one or more DL coverage enhancementtechniques comprise using different sets of control channel elements(CCEs) to transmit versions of the downlink channel in differentsubframes, and wherein locations of the different sets of CCEs in thedifferent subframes are linked.
 26. The method of claim 1, wherein theone or more DL coverage enhancement techniques comprise using a samedecoding candidate for transmitting the downlink channel in eachsubframe in a bundle of subframes.
 27. The method of claim 1, whereinthe one or more DL coverage enhancement techniques comprise transmittingthe downlink channel in a bundle of subframes and wherein a subframeoffset for a starting subframe in the bundle is determined at least oneof semi-statically or dynamically.
 28. The method of claim 27, whereinthe subframe offset for the starting subframe in the bundle iscell-dependent.
 29. The method of claim 1, wherein the one or more DLcoverage enhancement techniques comprise transmitting the downlinkchannel in a bundle of subframes and wherein a size of the bundle is atleast one of fixed or semi-statically configured.
 30. The method ofclaim 1, wherein the one or more DL coverage enhancement techniquescomprise transmitting the downlink channel in a bundle of subframes andwherein one or more physical layer (PHY) operations for transmitting aversion of the downlink channel vary in different subframes in thebundle.
 31. The method of claim 1, wherein the one or more DL coverageenhancement techniques comprise transmitting the downlink channel in abundle of subframes and wherein a size of the bundle is dynamicallyconfigured.
 32. The method of claim 1, wherein the one or more DLcoverage enhancement techniques comprise transmitting the downlinkchannel in a bundle of subframes and wherein one or more physical layer(PHY) operations for transmitting a version of the downlink channel arethe same in different subframes in the bundle.
 33. The method of claim1, wherein utilizing the one or more DL coverage enhancement techniquescomprises utilizing a first technique for a control channel andutilizing a second technique for a data channel for the first type ofUEs.
 34. The method of claim 1, wherein cross-subframe scheduling isutilized, such that a control channel sent in a first subframe schedulesa data transmission in a subsequent subframe.
 35. The method of claim 1,wherein the one or more DL coverage enhancement techniques compriseutilizing additional beamforming gain.
 36. The method of claim 1,wherein different DL coverage enhancement techniques are used for DLchannels transmitted in different decoding candidates.
 37. An apparatusfor wireless communications, comprising: means for identifying a firsttype of one or more user equipments (UEs) that is to receive enhanceddownlink (DL) coverage relative to a second type of UEs; and means forutilizing one or more DL coverage enhancement techniques whencommunicating with the first type of UEs, the one or more DL coverageenhancement techniques designed to adjust at least for reduced DLprocessing gain of the first type of UEs relative to the second type ofUEs.
 38. The apparatus of claim 37, wherein the reduced DL processinggain is due to at least one of: a reduced number of receive chainsrelative to the second type of UEs; reduced downlink transmission power;or narrower bandwidth operation relative to the second type of UEs. 39.The apparatus of claim 37, wherein the one or more DL coverageenhancement techniques comprise reducing a payload size of one or morecontrol channels when transmitting to the first type of UEs relative toa payload size of the same control channels when transmitting to thesecond type of UEs.
 40. The apparatus of claim 39, wherein: a firstpayload size is used when transmitting a unicast message of a first typeof control channel; and a second payload size is used when transmittinga non-unicast message of the first type of control channel.
 41. Theapparatus of claim 37, wherein the one or more DL coverage enhancementtechniques comprise increasing resources available for one or morecontrol channels to support a reduced coding rate.
 42. The apparatus ofclaim 41, wherein the increase in resources is relative to a number ofresources available when transmitting the same control channels to thesecond type of UEs.
 43. The apparatus of claim 41, wherein the sameinformation is repeated in different sets of resource elements (REs) ofthe increased resources.
 44. The apparatus of claim 41, furthercomprising means for receiving signaling indicating one or moresubframes in which a control channel is to be transmitted using theincreased resources.
 45. The apparatus of claim 37, wherein the one ormore DL coverage enhancement techniques comprise transmission timeinterval (TTI) bundling wherein redundant versions of a downlink channelare transmitted over a bundle of multiple DL subframes.
 46. Theapparatus of claim 45, wherein the bundle comprises N consecutive DLsubframes.
 47. The apparatus of claim 45, wherein the bundle comprises Nconsecutive non-Multimedia Broadcast Single Frequency Network(non-MBSFN) DL subframes.
 48. The apparatus of claim 45, whereindifferent numbers of resource blocks (RBs) are used to transmit thedownlink channel for DL subframes in the bundle with and without adownlink pilot time slot (DwPTS).
 49. The apparatus of claim 45, whereinthe downlink channel comprises a physical downlink shared channel(PDSCH).
 50. The apparatus of claim 49, wherein the TTI bundlingcomprises transmitting a single transport block (TB) over multiplesubframes.
 51. The apparatus of claim 50, wherein the TB is transmittedin each subframe of the bundle using a same modulation and coding scheme(MCS).
 52. The apparatus of claim 50, wherein the TB is transmitted ineach subframe of the bundle using a same number of resource blocks(RBs).
 53. The apparatus of claim 52, wherein the TB is transmitted ineach subframe of the bundle using different locations of resource blocks(RBs).
 54. The apparatus of claim 45, wherein a scheduling timingbetween a control channel and a corresponding physical downlink sharedchannel (PDSCH) transmitted via the TTI bundling is determined based ona first subframe in the bundle.
 55. The apparatus of claim 45, wherein ahybrid automatic repeat request (HARQ) timing between a physicaldownlink shared channel (PDSCH) transmitted via the TTI bundling and acorresponding HARQ response is determined based on a last subframe inthe bundle.
 56. The apparatus of claim 45, wherein a number of hybridautomatic repeat request (HARQ) processes supported is dependent on aTTI bundling size.
 57. The apparatus of claim 37, wherein the one ormore DL coverage enhancement techniques comprise using a sameaggregation level for transmitting the downlink channel in each subframein a bundle of subframes.
 58. The apparatus of claim 37, wherein the oneor more DL coverage enhancement techniques comprise using differentaggregation levels for transmitting the downlink channel in differentsubframes in a bundle of subframes.
 59. The apparatus of claim 58,wherein an aggregation level used in a subframe is dependent onavailable resources in that subframe.
 60. The apparatus of claim 37,wherein the one or more DL coverage enhancement techniques comprisetransmitting the downlink channel in a bundle of subframes and wherein aversion of the downlink channel in each subframe in the bundle isindividually coded, modulated, and mapped to resources.
 61. Theapparatus of claim 37, wherein the one or more DL coverage enhancementtechniques comprise using different sets of control channel elements(CCEs) to transmit versions of the downlink channel in differentsubframes and wherein locations of the different sets of CCEs in thedifferent subframes are linked.
 62. The apparatus of claim 37, whereinthe one or more DL coverage enhancement techniques comprise transmittingthe downlink channel in a bundle of subframes and wherein a samedecoding candidate is used for transmitting the downlink channel in eachsubframe in the bundle.
 63. The apparatus of claim 37, wherein the oneor more DL coverage enhancement techniques comprise transmitting thedownlink channel in a bundle of subframes and wherein a subframe offsetfor a starting subframe in the bundle is determined at least one ofsemi-statically or dynamically.
 64. The apparatus of claim 63, whereinthe subframe offset for the starting subframe in the bundle iscell-dependent.
 65. The apparatus of claim 37, wherein the one or moreDL coverage enhancement techniques comprise transmitting the downlinkchannel in a bundle of subframes and wherein a size of the bundle is atleast one of fixed or semi-statically configured.
 66. The apparatus ofclaim 37, wherein the one or more DL coverage enhancement techniquescomprise transmitting the downlink channel in a bundle of subframes andwherein one or more physical layer (PHY) operations for transmitting aversion of the downlink channel vary in different subframes in thebundle.
 67. The apparatus of claim 37, wherein the one or more DLcoverage enhancement techniques comprise transmitting the downlinkchannel in a bundle of subframes and wherein a size of the bundle isdynamically configured.
 68. The apparatus of claim 37, wherein the oneor more DL coverage enhancement techniques comprise transmitting thedownlink channel in a bundle of subframes and wherein one or morephysical layer (PHY) operations for transmitting a version of thedownlink channel are the same in different subframes in the bundle. 69.The apparatus of claim 37, wherein the means for utilizing the one ormore DL coverage enhancement techniques is configured to utilize a firsttechnique for a control channel and to utilize a second technique for adata channel for the first type of UEs.
 70. The apparatus of claim 37,wherein cross-subframe scheduling is utilized, such that a controlchannel sent in a first subframe schedules a data transmission in asubsequent subframe.
 71. The apparatus of claim 37, wherein the one ormore DL coverage enhancement techniques comprise utilizing additionalbeamforming gain.
 72. The apparatus of claim 37, wherein different DLcoverage enhancement techniques are used for DL channels transmitted indifferent decoding candidates.
 73. An apparatus for wirelesscommunications, comprising: at least one processor configured to:identify a first type of one or more user equipments (UEs) that is toreceive enhanced downlink (DL) coverage relative to a second type ofUEs; and utilize one or more DL coverage enhancement techniques whencommunicating with the first type of UEs, the one or more DL coverageenhancement techniques designed to adjust at least for reduced DLprocessing gain of the first type of UEs relative to the second type ofUEs; and a memory coupled to the at least one processor.
 74. Anon-transitory computer-readable medium for wireless communications, thenon-transitory computer-readable medium having instructions storedthereon, the instructions executable by one or more processors for:identifying a first type of one or more user equipments (UEs) that is toreceive enhanced downlink (DL) coverage relative to a second type ofUEs; and utilizing one or more DL coverage enhancement techniques whencommunicating with the first type of UEs, the one or more DL coverageenhancement techniques designed to adjust at least for reduced DLprocessing gain of the first type of UEs relative to the second type ofUEs.